System and method for acquiring marine seismic data using a vibrator

Abstract

Described herein is a method for acquiring data using a marine vibrator towed by a vessel, the method comprising: obtaining data comprising at least one nominal pre-plot position in a horizontal plane; monitoring a position of the marine vibrator in the and a speed of the vessel; determining an offset between the position of the marine vibrator and the nominal pre-plot position in the towing direction; based on the offset and the vessel speed, adjusting one or more survey parameters and driving the vibrator with a series of one or more sweeps so that a predetermined frequency in the sweep or a subsequent sweep is emitted when the position of the vibrator is within a maximum distance of the nominal pre-plot position.

What is claimed is: 
     
       1. A method for acquiring marine seismic data with a vibrator towed by a vessel, the method comprising:
 obtaining data comprising a plurality of nominal and regularly spaced pre-plot positions; 
 monitoring the speed of the vessel and a position of the vibrator; 
 based on the speed of the vessel, setting an initial sweep, comprising an active sweep period and zero or more silent portions, wherein the total length of the sweep is equal to the time taken for the vibrator to travel from one nominal pre-plot position to the next nominal pre-plot position; 
 driving the vibrator with the initial sweep parameters; 
 at the start of every N th  sweep, where N is equal to or greater than one, determining an offset between the actual vibrator position the nominal pre-plot position in the inline direction; 
 if the offset is above a threshold distance, adjusting the length of the sweep so that the subsequent sweep is started within a predetermined distance of its nominal pre-plot position. 
 
     
     
       2. The method of  claim 1 , wherein N is equal to or greater than 2. 
     
     
       3. The method of  claim 1 , wherein the length of the silent portions is between 0 ms and 2000 ms. 
     
     
       4. The method of  claim 3 , wherein the length of the silent portions is between 0 ms and 1000 ms. 
     
     
       5. The method of  claim 1 , wherein adjusting the length of the sweep comprises adjusting the length of one or more of the one or more silent portions of the sweep. 
     
     
       6. The method of  claim 1 , wherein adjusting the length of the sweep comprises adjusting the length of the active portion of the sweep. 
     
     
       7. The method of  claim 1 , comprising adjusting the amplitude of the sweep such that the energy emitted at each sweep is substantially the same. 
     
     
       8. The method of  claim 1 , wherein the method is a method for acquiring 4D compatible seismic data. 
     
     
       9. A non-transitory computer readable medium including computer executable instructions, wherein the instructions, when executed by a processor, cause the following operations to be performed:
 monitoring a position of the marine vibrator and the speed of the vessel; 
 determining an offset between the position of the marine vibrator and its nominal pre-plot position in the inline direction; 
 
       based on said offset and the vessel speed, adjusting one or more survey parameters and driving the vibrator with sweeps so that a predetermined frequency is emitted when the position of the vibrator is within a maximum distance of the nominal pre-plot position. 
     
     
       10. A non-transitory computer readable medium including computer executable instructions, wherein the instructions, when executed by a processor, cause the following operations to be performed:
 obtaining data comprising a plurality of nominal and regularly spaced pre-plot positions; 
 monitoring the speed of the vessel and a position of the vibrator; 
 based on the speed of the vessel, setting an initial sweep, comprising an active sweep period and zero or more silent portions, wherein the total length of the sweep is equal to the time taken for the vibrator to travel from one nominal pre-plot position to the next nominal pre-plot position; 
 driving the vibrator with the initial sweep parameters; 
 at the start of every Nth sweep, where N is equal to or greater than one, determining an offset between the actual vibrator position the nominal pre-plot position in the inline direction; 
 if the offset is above a threshold distance, adjusting the length of the sweep so that the subsequent sweep is started within a predetermined distance of its nominal pre-plot position.